A diesel particulate filter (hereinafter, referred to as DPF), for example, is known as a filter for collecting particulate matter (hereinafter, referred to as PM) in an exhaust gas emitted from a diesel engine.
The DPF can only collect a limited amount of PM, and therefore a forced regeneration needs to be performed to periodically burn and remove accumulated PM. The forced regeneration is performed by supplying unburned fuel, primarily hydrocarbon (“HC”), to an oxidation catalyst on an upstream side of an exhaust passage by means of in-pipe injection or post-injection, and raising the exhaust gas temperature to a PM-burning temperature with heat produced upon oxidation.
For example, Patent Literature 1 discloses an exhaust gas purification system that performs a forced regeneration by raising the temperature of a DPF by means of post-injection as the pressure difference across the DPF between the upstream side and the downstream side of the exhaust passage reaches or exceeds a predetermined value.